Insect-pathogenic fungi are important natural enemies of insect pests but their dynamics in the soils of different agroecosystems are incompletely understood. In the present study, the seasonal occurrence and species diversity of insect-associated fungi in soil were investigated by baiting soil samples with larvae of Galleria mellonella. The survey included insect-pathogenic fungi, opportunistic insect pathogens, and secondary colonizers of insect cadavers. Soil samples from two habitat types (field crops and orchards) were collected from 2004 to 2005 at 2-month intervals except during wintertime. A total of 29 species were isolated and identified, with 25 species in field crop soils and 20 species in orchard soils. Although the common insect-pathogenic species, such as Beauveria bassiana, Metarhizium anisopliae var. anisopliae, and Paecilomyces fumosoroseus (Ascomycota: Hypocreales), were detected in both field crop and orchard soils, their frequency in the two agroecosystems differed significantly: B. bassiana and P. fumosoroseus were more frequently detected in orchard soils, while M. anisopliae var. anisopliae was more frequently detected in field crop soils. The diversity of insect-pathogenic fungi was greater in field crop soil than in orchard soil. The number of Galleria larvae that died from fungal infection was larger in orchard soil than in field crop soil. B. bassiana was the most abundant species in orchard soil, and the number of larvae killed by B. bassiana was larger in June and December than in April and August. However, Mucor spp. (opportunistic pathogens) were the most abundant species in field crop soils, and the number of larvae killed by them was larger in August than at any other time of the year.